U.S. Pat. No. 2,420,550 issued to R. Miller on May 13, 1947 shows a fuel injector wherein the injector plunger 57 has equal opposite end areas exposed to an injection chamber 46 and a control chamber 52. A valve spool 14 is mechanically oscillated by engine-driven cam 8 to alternately connect control chamber 52 to the pressurized fuel supply 2 or the drain 69.
The patentee varies the start of injection and quantity of injection by means of a rack 35 and pinion 32. Rack movement rotates valve spool 14 so that relatively wide or relatively narrow sections of the flow control grooves 19 and 27 register with the various ports in valve housing 3.
The system shown in the Miller patent is advantageous in that relatively high fuel supply pressures can be used without premature opening or delayed closing of the discharge orifice 44 (FIG. 1 of the patent). However the Miller patented system lacks the capability for independent adjustment of the injection start time and injection quantity. In the Miller system movement of rack 35 simultaneously varies the start of injection (by groove 27) and the end of injection (by groove 19). At full load setting of rack 35 the injection might begin at approximately twenty five degrees before top dead center and end at approximately five degrees after top dead center. At light load setting of rack 35 the injection might begin at approximately twelve degrees before top dead center and end at approximately two degrees before top dead center.
The present invention involves a redesign of the Miller system so that start of injection and quantity of injection can be independently varied or adjusted. The air is to improve fuel-air mixing and combustion over a wide range of operating conditions. The sought-for improvement is obtained by operating the spool valve with an electric solenoid rather than by mechanical cams or cranks. Present day electronics are at the stage where electrical transducers can be utilized to very accurately start and end the flow of current to each solenoid (at each injector). It thus now becomes practical to electronically vary the start of injection and/or end of injection independently, thereby providing improved engine operation over a range of conditions.
The present invention also aims at reducing the piping complexity and housing complexity evident in the Miller patent arrangement. In our improved version the control valve (solenoid-operated) is disposed within the same housing as the injector plunger, thereby enabling various passages to be formed internally as straight drilled holes rather than externally as extraneous tubes and tube fittings. The accommodation of the control valve and injector plunger within a single housing reduces fabrication cost, overall housing size, and maintenance difficulties (especially when it becomes necessary to troubleshoot, and/or remove injectors, and/or install new injectors).
The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without payment to us of any royalty thereon.